# AQA Topic 3 - Quantitative Chemistry 9-1

• Created by: Grace
• Created on: 02-05-18 20:53
What is relative formula mass? what is its symbol?
All compounds have relative formula mass, which is just the relative atomic masses of all the atoms in the molecular formula added together. Mr
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How can you calculate the percentage mass of an element in a compound?
Percentage mass of an element in a compound = (Relative atomic mass x no. of atoms of that element÷ Relative formula mass) x100
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Define a mole
One mole of any substance is an amount of that substance that contains an Avogadro number of particles
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6.02 x 10 to the power of 23
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What does the Avogadro constant say?
That the mass of that number of atoms or molecules of any substance is exactly the same number of grams as the Ar or Mr
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If carbon has an Ar of 12, how much would one mole weigh?
12g
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What is the formula to find moles?
Number of moles = Mass (g) ÷ Mr (of said element or compound)
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What happens to mass in a chemical reaction?
Mass is always conserved as no atoms are destroyed or created
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What is the likely explanation if a mass seems to change?
That a gas is involved, either it is a reactant so the initial mass of it isn't counted or its a product so when released the mass 'decreases'
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How would you write a balanced equation when given the masses of elements?
Find the Mr of the substances and then consequently find the moles for each. Divide all the moles by the smallest mole of the substances and then the final no.s you can put in front of the formulas
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Define the term Limiting Reactant
Reactions stop when a reactant is used up and limits the amount of product that's formed
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What does it mean when a reactant is left in excess?
It means that one of the reactants has been used up so the other reactants are in excess (not needed)
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Complete the sentence: The amount of product formed is _____ proportional to the amount of ______ reactant
1. Directly 2. Limiting
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What is the mass of product also known as?
The yield of a reaction
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Refer to Page 43 'Aluminium Oxide' example
N/A
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What does one mole of any gas contain at 20°C
24dm cubed
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Complete the sentences: At the same temperature and _____, equal numbers of ____ of any ___ will occupy the same ____
1. Pressure 2. Equal 3. Gas 4. Volume
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What does r.t.p mean?
Room temperature and pressure
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What is the equation for finding the volume of gas at r.t.p?
Volume of gas (dm3) = Mass of gas ÷ Mr of gas x 24
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Define concentration
The amount of a substance - the mass or the number of moles - in a certain volume of a solution
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How is concentration increased?
The more solute (the substance thats dissolved) there is in a given volume the more concentrated the solution is
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What is the equation for concentration involving mass?
Concentration = Mass of solute ÷ Volume of solvent (must be in dm3)
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What is the equation for concentration involving moles?
Concentration = Number of moles of solute ÷ Volume of solvent (must be in dm3)
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How can you get from cm3 to dm3?
Divide the volume by 1000
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What equation might would you need to calculate titration?
Concentration = moles ÷ volume
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Refer to page 47 for the 1st example
N/A
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How do you convert from mol/dm3 to g/dm3?
First find the concentration in mol/dm3 then convert using moles = mass x mr
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What is atom economy?
Percentage of reactants forming useful products
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What does 100% atom economy mean?
That all the atoms in the reactants have been turned into the desired (useful) products therefore the higher atom economy the 'greener' (efficient) the process
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Give the equation for atom economy
Atom economy = (Mr of Useful products ÷ Mr of all reactants) x 100
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Why is low atom economy bad?
Reactions with low atom economy use up resources quickly and at the same time they make a lot of waste materials that have to be disposed of. This makes the reactions unsustainable plus they are not profitable and raw materials are expensive
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How can you economise low atom economy?
Due to there being multiple ways to get the desired products you can still use low atom economy reactions by coming up with a reaction that makes useful 'by products' instead of useless ones
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What reactions tend to have high atom economy?
Ones that only have one product as the more reactions = likely a lower atom economy
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When choosing a reaction what should be considered?
1. Atom Economy 2. Percentage Yield 3. Rate of Reaction 3. Position of Equilibrium for reversible reactions
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What does percentage yield do?
It compares actual and theoretical yield
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Define yield
The amount of product you get
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How do you increase yield?
The more reactants = more products = higher actual yield
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Give the equation for percentage yield
Percentage yield = (Mass of actual product ÷ Max theoretical mass of product) x 100
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Why do industrial processes need a high percentage yield?
Reduce waste and reduce costs
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Why are yields always less than 100%?
Some products or reactants always gets lost which depends on what sort of reaction it is and the apparatus used
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Name and describe the three common problems of getting high percentage yields (1)
1. Not all reactants react to make a product - In reversible reactions the products turn back into reactants so the yield will never be 100% i.e the Haber Process 2. There might be side reactions - The reactants might react with gases in the air or
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Name and describe the three common problems of getting high percentage yields (2)
Impurities in the reaction mixture so they end up forming extra products other than the ones you want 3. Some product may be lost when you separate it from the reaction mixture - When a liquid is filtered to remove solids either a little bit of solid
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Name and describe the three common problems of getting high percentage yields (3)
or liquid is lost and when transferring it from one container to another some is lost
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## Other cards in this set

### Card 2

#### Front

How can you calculate the percentage mass of an element in a compound?

#### Back

Percentage mass of an element in a compound = (Relative atomic mass x no. of atoms of that element÷ Relative formula mass) x100

Define a mole

### Card 5

#### Front

What does the Avogadro constant say?